It is important not to go too fast and to consider all the following points before starting the work...
Location
Its location must be carefully defined. The ideal situation should be half-shaded, while avoiding being under a tree because of the risk of its roots spreading out and damaging the walls and because of the leaves that will not fail to land in the water.
Remember to leave a strip of land around the pond of about 1 meter wide which will be used for access, installation of stones or plants.
Shape and size of the pond
If the pond is too small, it will suffer from too much thermal variation if you intend to put fish in it.
Concerning the depth, everything depends on the surface of the ground, knowing that it is desirable to have not too steep dimensions, and a slope in step with a step every 20-30 cm and a width of 10-20 cm. A bottom of 60 to 80 cm will allow your fish to spend a comfortable winter and the summer to avoid that the water is too hot. 60 cm will be enough if you have a pump ensuring a water circulation in winter.
The steps of different depths will allow you to place pots of plants or flowers according to their size.
Let's identify the different zones:
The border zone between 10 and 20 cm, allows the development of small plants whose roots appreciate the mud and water. It is also the place where insects develop between the roots of the plants and where the fry come to take refuge, thus sheltered from the parents often inclined to devour their offspring.
The shallow zone between 20 and 40 cm; in this zone, many plants for plants like reeds, water iris, ... We can also plant submerged plants.
The deep zone, refuge of the fishes the winter, it is also in this zone that one will deposit the feet of water lilies.
Filtration
Have you thought about filtration? If you intend to put fish in your pond, it is preferable to install a filter. It allows to keep all its clarity to the water, otherwise it will have a tendency to green very quickly. It also ensures a circulation of water and thus an oxygenation of water by these movements on the surface and the winter, it prevents the ice from forming.
You can install it in a special tank outside the pond with lava stones to ensure a biological filtration.
If you are not interested in a filter, you may want to consider a pump to circulate the water from one side to the other and perhaps feed a fountain, waterfall, etc. ... This will energize the pond and delight you with its chirping, but beware of the neighbors, a torrent may not be to their taste!
Lining the pond
First, you will have stabilized the walls with a layer of gravel, then a layer of sand and finally a little cement to harden the whole. Thus stiffened, the walls will resist better over time, to the attacks of the roots and to the settlement of the ground.
The walls must then be sealed, and different materials are possible:
The preformed pond, in this case, forget what was said before.
The concrete; several layers of cement more and more fine will be necessary to ensure a perfect sealing.
The PVC liner is certainly the least expensive and most durable, so... To calculate the size of the liner, add 2 meters in width and 2 meters in length for a 60 cm deep pond with 30 cm edges.
The rubber cover, more expensive than the PVC cover, will last longer because it is more flexible.
Whatever cover you use, put a garden felt underneath.
Check filling
A check fill for water tightness and levels is necessary to ensure that everything is in order. It is still possible to make some adjustments to the edges of the pond.
This is also an opportunity to test your filtration system.
Let it run for a few weeks.
